noun: A windowlicker is a derogatory, informal description of someone with severe learning disabilities and/or a physical incapacity which renders them helpless when faced with the prospect of seeing a stranger through a window without smearing their mucus covered tongues all over the glass, possibly as some kind of retard greeting.

Alternatives are 'spaz' or 'mongole'.

Small child: Tee hee, look at those windowlickers!!!!

Mother: You shouldn't be unkind, they are people too

Small child: Eugh! Look at that one windowlicker with the snotty nose!

(derogatory) ~ sl.: euphemism for a person of mentally challenged status. Etymology: C20 - Derived from the stereotyped behaviour of mentally challenged people, observed to place their open mouths into prolongued contact with the external windows of public or private transport on which they are seated.

It is offensive and wrong to name a person people who is mentally challenged a 'window licker' or a 'retard'.